Tin ore treating process

ABSTRACT

A method of beneficiating crushed and ground tin oxide ores, including concentrates, by first sulfidizing to produce stable tin sulfides SnS2, Sn2S3 and SnS, and then, after initial separation of magnetic iron sulfide constituents, subjecting to progressive and selective flotation to remove the several tin sulfides formed. Flotation is ordinarily first carried out under alkaline conditions and then under conditions of increasing acidity. Nonmagnetic iron sulfide may be removed by flotation under mildly acid conditions and any residual magnetic iron sulfide may be removed by further magnetic separation. When elemental sulfur is used as the sulfidizing agent, as when pyrite is used as the sulfur source, iron oxide minerals in the tin ore or concentrates are preferentially sulfidized to form magnetic and nonmagnetic iron sulfide components. This characteristic enables the iron oxide minerals to be separated from the tin oxide ore by magnetic separation and progressive flotation.

United States Patent I 3,642,464 Dorenield et al. 1 Feb. 15, 1972 [s41TIN ORE TREATING PROCESS 636,356 4/1950 Great Britain ..74/2

' ..209 167 [72] Inventors: Adrian C. Dorenteld, Brooklyn Center,l059476 2/1967 Great Bmam I Minn.; Fernando Jorge Dick, Oruro, Bolivia,South America; Strathmore R. B. OTHER PUBLICATIONS Cooke, Robbinsdale,Minn. [73] Assignee: The Regents o the University of Mim Chemabstracts,Vo1.66, 1967,P.5484,58030p nesota Mmneapohs Mmn' PrimaryExaminer-Frank W. Lutter [22] Filed: Dec. 9, 1968 AssistantExaminer-Robert Halper [2]] App] No 782 064 Attorney-Kurd, Braddock &Bartz [57] ABSTRACT [52] US. Cl ..7S/2, 209/ l 1,220%9//l3697, A methodof beneficiating crushed and ground tin oxide ores, includingconcentrates, by first sulfidizing to produce stable g F {3; tinsulfides sns,, sn s nd SnS, and then, after initial separa.

tion of magnetic iron sulfide constituents, subjecting to 75/1progressive and selective flotation to remove the several tin sulfidesformed. Flotation is ordinarily first carried out under [56] ReferencesCited alkaline conditions and then under conditions of increasing U ESTATES PATENTS acidity. Nonmagnetic iron sulfide may be removed byflotation under mildly acid conditions and any residual magnetic1,513,812 11/1924 Henders n t iron sulfide may be removed by furthermagnetic separation.

1,312,668 8/1919 Bacon When elemental sulfur is used as the sulfidizingagent, as when 2,424,402 7/ 1947 Loane....

----- pyrite is used as the sulfur source, iron oxide minerals in theMercade tin ore o concentrates are preferentially sulfidized tofemmagnetic and nonmagnetic iron sulfide components. This FOREIGNPATENTS 0R APPLICATIONS characteristic enables the iron oxide mineralsto be separated 9,508 6/1913 Australia ..209/167 fr m he tin oxide oreby magnetic separation and progressive 26,019 12/1910 Great Britain....209/ 167 ta 252,414 1 1963 Australia ..75 2

I 18 Claims, 2 Drawing Figures Lea I N DINHSTRQNGLY MAGNETIC MATERIALREMOVED] SULFIDIZATION MAGNETIC L MAGNETIC SEPARATION CONCENTRATESULFIDIZED TIN ORE FLOTATION AT HS P-Ensz CONCENTR/Elq snszsn,s;-sns-Fes MIX AND CONDITION FLOTAT'ON AT CONCENTRATE WITH GLUE SPESJ'T5H5 FLOTATION AT PH2.8 CONCENTRATE L IFLOTATIOII AT HTHlRON suLFIDFT]TIN SULFIDE CONCENTRATE OPTIONAL MAGNETIC SEPARATION SULF'DE IFINAL TINSULFIDE CONCENTRATEI TIN ORE TREATING PROCESS This invention relates tothe treatment of low-grade tin ore including concentrates, hereinafterreferred to simply as ores, in order to make them more amenable toflotation methods of concentration, and to the subsequent concentrationof those ores by flotation. More particularly, the invention relates tothe sulfidization of low-grade tin oxide ores by treatment of the orewith sulfur or sulfur-bearing material in gaseous or vapor form atelevated temperatures in a nonoxidizing or reducing atmosphere and,thereafter, concentrating the resulting sulfides by progressive andselective flotation methods.

The art is crowded with various proposals for effecting the flotationand separation of nonsulfide ores by first superficially converting themetallic nonsulfide minerals in aqueous suspension into sulfides andthen subjecting the sulfidized ores to flotation methods ofconcentration. These prior processes where directed at the recovery oftin have not found acceptance by the mining industry for variousreasons, because they have been too expensive or result in low-gradeproducts or produce low yields or otherwise are not economically andpractically feasible.

As our civilization advances and sources of high-grade ores becomedepleted, it becomes necessary to be able to treat ore bodies ofever-decreasing quality. In the constant search for economically andpractically feasible methods of treating lowgrade ores, it is useful tostudy and reevaluate past failures with the objective of modifying andimproving them in order to produce new, useful and valuable methods ofore treatment and recovery. I

It is the particular object of this invention to provide a process forthe separation and recovery of oxide tin (cassiterite) ores by firstcrushing the ore, followed by magnetic separation of conventionalmagnetic materials, and exposing the nonmagnetic ore to the effects ofsulfur or sulfurbearing material in gaseous or vapor form in anonoxidizing or reducing atmosphere at elevated temperatures, removingmagnetic iron compounds by magnetic separation, and then separating theresulting tin sulfides by progressive and selective flotationprocedures. 7

Other objects of the invention will become apparent as the descriptionproceeds.

. To the accomplishment of the foregoing and related ends, thisinvention then comprises the features hereinafter fully described andparticularly pointed outin the claims, the following description settingforth in detail certain illustrative embodiments of the invention, thesebeing indicative, however, of but a few of the various ways in which theprinciples of the invention may be employed.

The invention is illustrated by the accompanying drawings which show inschematic flow sheet form the steps by which the beneficiation processesare carried out.

Flotation has long been recognized as an effective and economicalprocedure for concentrating natural sulfide ores. However, mostnonsulfide metallic ores are not readily amenable to concentration byflotation. Tin sulfides rarely occur in nature. The most common tinmineral in the tin ores is cassiterite, a tin dioxide. It is notamenable to sulfide mineral flotation without prior treatment. Thepresent invention resides in the development of a simple, effective andeconomical method of sulfidization using sulfur or sulfur-bearingmaterial in gaseous or vapor form in a nonoxidizing or reducingatmosphere, followed by magnetic separation of magnetic constituents andprogressive and selective flotation.

The ore is crushed or ground before sulfidization although the particlesize is not critical, except that the tin mineral should be sufficientlyliberated so as to be exposed to the sulfurgas reactions. The ores aredesirably crushed. to one-eighth inch particles or less and preferablyare crushed to about 20- mesh size (about one thirty-second of an inch).Sulfidization proceeds somewhat more rapidly with smaller ore particles,and for this reason, somewhat smaller particle. sizes are preferred.

The essence of the sulfidization step of the present invention istreatment of the ore with sulfur or sulfur-bearing material in gaseousor vapor form in a nonoxidizing or reducing atmosphere. The sulfur gasmay be generated by heating elemental sulfur above its boiling point orby heating a sulfurcontaining compound high enough to cause it todecompose enough to yield gaseous sulfur. Sulfur-containing sourcesacceptable for this process include iron pyrite, marcasite, hydrogensulfide, and the like. Certain minerals associated with cassiteritecontain sulfur in the form of iron pyrites or other metal sulfides orother decomposable sulfur compounds as impurities. When this occurs,some or all of the sulfur already present may be yielded when heated foruse in the sul fidization step as gaseous sulfur.

Because the sulfur should be maintained in gaseous form, thesulfidization s'tep must be carried out at elevated temperatures. In thecase where relatively pure sulfur is used as the source of sulfur gas,the temperature must be near or above the boiling point of sulfur (445C.). in the case of iron pyrite, temperatures of the order of about 720C. are necessary to decompose the sulfide andliberate half of the sulfurin the pyrite as gas. In the case where hydrogen sulfide is used as thesource of sulfur, and because hydrogen sulfide is a gas at the operatingconditions, conversion of tin oxide to tin sulfide can be accomplishedover a broader range of temperatures. Where lower temperatures areemployed, the time required is longer for conversion of the tin oxide toa sulfide form.

It has been known that the sulfidization of tin oxide (cassiterite)produces three stable tin sulfides: SnS Sn S and SnS. It is ourdiscovery that these three sulfides have different flotationcharacteristics, and that the SnS is the preferred form. It has beenfound that the critical upper temperature limit for the production ofthe SnS is about 600 C. Above this temperature the production of Sn Sand SnS predominates. lf sulfidization of the ore is carried out athigher temperatures so that Sn S and SnS are produced, our processteaches that the product can then be soaked in a sulfur vapor atmosphereat a lower temperature to produce the preferred outermost coating of SnSThe sulfidization reaction is carried out in the presence of anonoxidizing or reducing atmosphere. Suitable nonoxidizing or reducingatmospheres, such as hydrogen, methane, carbon monoxide and natural gas,or inert or neutral gases, such as nitrogen or the like, may be used.The sulfidized ore is cooled in a nonoxidizing or reducing atmosphere orotherwise cooled in such a manner as to avoid reoxidation.

In this process sulfidization is a function of the amount of sulfur gaspresent, the period the material is exposed to the gas, and theoperating temperature. The quantity of sulfur gas present need only bethat amount which permits the formation of a sulfide surface coating onthe ore particles so that the material will act as a sulfide in theflotation step; any additional sulfur in the gas will not harm thereaction nor will it add any significant benefit. With respect totreatment times, good conversion and subsequent flotation recovery rateshave resulted in treatments ranging from about 5 minutes to about 1hour; a typical treatment time is about 10 to 20 minutes. With respectto temperature, conversion of the tin oxides to sulfides begins at about200 C. with the process operating to best advantage in the range fromabout 400 to about 600 C.

The sulfides produced as a result of the sulfidization step are firstsubjected to magnetic separation treatment to remove magneticconstituents, principally magnetic iron sulfide, and thereafter they areconcentrated by flotation procedures.

Flotation procedures for the concentration of sulfide minerals are wellknown. Briefly, the flotation method of separation depends uponselective or preferential floating of one or more materials from othermaterials with which it, or they, are associated. Ore is usually mixedwith water in the proportion of about 1 part by weight of ore to 4 or 5parts by weight of water. Small amounts, about 0.1 to 5 pounds per tonof ore, of desired reagents are added to the pulp, each having aspecific function and referred to as collectors, frothers, pH

modifiers, depressants, and activators. Collecting agents reactpreferentially with the surfaces of sulfide minerals in such a mannerthat when gas bubbles come into contact with these coated minerals,these minerals either stick to the bubbles or tend to do so. Thenoncoated mineral particles do not adhere to the gas bubbles. The usualgas employed to make bubbles is air. Compounds used to produceparticular types of froths (called frothers) are also added to thegulps. Besides collectors and frothers, other chemicals are used tocontrol collector reactions with particular sulfides or froth reactionsor reactions among the minerals themselves. There is voluminousliterature, both in patents and technical periodicals, which listsinnumerable variants and combinations of chemicals.

Typical collectors are potassium or sodium alkyl xanthates and othersulfliydryl types of collectors. Potassium amyl xanthate is a commoncollecting agent. Another common collecting agent is marketed under thetrade name Aerofloat, a thio phosphate organic. The general structuralformula is:

no SH(orM) in which R is an alkyl or aryl radical and M an alkali metalor ammonium ion. Typical frothing agents are crude cresylic acid, higheralcohols, such as amyl alcohols, steam distilled pine oil and the like.Typical pH modifiers are soda ash, sodium hydroxide, lime, sulfuric acidand the like. Typical depressants are alkali cyanides, starches,sulfites of various types, zinc sulfate, chromates and the like. Typicaldispersants are sodium silicates, lignin sulfates and the like.Activators are metal ions added to alter the surfaces ofa sulfidemineral. This altered surface in turn may then be coated by a collector.

After the ore, properly ground, is in suspension in water and thereagents added for flotation, gas bubbles are made by machines wellknown in the art in such a way that a froth phase forms on the surfaceof the agitate ore pulp. The froth containing the gas bubbles, whichtend to preferentially stick to or otherwise sort out the sulfideminerals preferentially, generally contains the sulfide minerals ofinterest.

According to the present invention, sulfidization followed by certainconcentration steps, results in ores that have been concentrated from 2to times their original metal content with recoveries, in some tests inexcess of 90 percent. Because the several stable tin sulfides formedduring sulfidization and contained in the aqueous pulp have differentflotation characteristics, progressive and selective flotation isnecessary for maximum recovery. The table appearing below sets forth thequalitative flotation characteristics of tin sulfides.

TABLE I Qualitative Flotation Characteristics ofTin Sulfideslhiophosphate organic amyl xanthate Alkaline Acid Alkaline Acid SnS pooroor poor good Sn,S poor poor poor good SnS good good poor good In orderto produce a tin concentrate which is acceptable to tin smelters, it isnecessary that the tin concentrate contain as little iron as possible.The upper limit of iron is dependent upon the smelters ability to acceptthat type of ore. The smelters blend these high-iron with low-iron ores.Such low-iron ores are in short supply. When the other iron minerals aresulfidized, along with the tin-containing mineral, magnetic andnonmagnetic iron sulfides are formed. The magnetic iron sulfide,although not readily floatable, reacts in the aqueous pulp to form asignificant concentration of iron ions. It has been discovered that ironions depress tin sulfides during flotation. Therefore it is important toremove the magnetic iron sulfides prior to the tin sulfide flotation.This can be accomplished by conventional magnetic separators. Thenonmagnetic iron sulfides float readily, and therefore float with thetin sulfides using xanthate in the acid pH range. These nonmagnetic ironsulfides are eliminated by a flotation step consisting of adding glue toa tin sulfide iron sulfide concentrate causing the tin sulfide to bedepressed and allowing the iron sulfide to enter the froth phase,forming an iron sulfide concentrate which is either in whole or in partdiscarded or recycled through sulfidization or flotation or both,depending upon its tin content.

The process of beneficiating tin oxide ores according to the presentinvention, as illustrated in the flow sheet, proceeds generally asfollows: The crude tin ore is crushed and ground and then sulfidized.Where sufficient magnetite is present, it is separated by magneticmeans. sulfidization is carried out in the presence of sulfur in gaseousform under completely nonoxidizing or reducing atmospheric conditions atan elevated temperature, preferably no greater than 600 C. Thesulfidized tin ore is cooled under nonoxidizing or reducing atmosphericconditions and then subjected to magnetic separation to remove anymagnetic iron sulfide which may be present.

When the objective is to float tin sulfides, the sulfidized tin ore,after magnetic separation, is subjected to a first flotation treatmentunder alkaline conditions between about pH 7.5 to 9, preferably at aboutpH 8, using a thiophosphate organic as the promoter. Cyanide may beadded to depress the iron minerals. The first tin concentrate, which isremoved as froth, contains predominantly SnS The pulp from the firstflotation treatment is then acidified to between about pH 4.5 to 5.5,preferably about pH 5, and conditioned with a xanthate. This second tinconcentrate, which is removed as froth, contains most of the ironsulfide remaining in the ore along with the balance of the SnS and someSn S and SnS. The pulp is then acidified further to between about pH 2and 3.5, preferably about pH 2.8 for optimum recovery, and conditionedwith xanthate. The froth making up this third tin concentrate containsthe balance of the Sn S and SnS.

The second tin concentrate from flotation at about pH 5 is then mixedwith the magnetic concentrate from the magnetic separation step andconditioned with glue. Flotation is carried out at between about pH 4.5and 5.5, preferably about pH 5. The iron sulfide separates in the froth,leaving a tin sulfide concentrate in the pulp. Because magnetic ironsulfides do not float as well as the nonmagnetic, any residual magneticiron sulfide remaining in this tin concentrate is extracted by furthermagnetic concentration. The product of this optional further magneticconcentration, if rich enough in tin, is recycled for retreatment.Otherwise, it is discarded along with the iron sulfide collected in thefroth from the preceding flotation treatment. The several tinconcentrates are then joined to produce a final product for smelting.

When the objective is to float iron sulfides from tin sulfides as afirst step and where elemental sulfur is used as the sulfidizing agent,then xanthates are used as the promoter. The flotation is conducted ineither a slightly alkaline pulp or slightly acid pulp to encourage theiron sulfides to float. Glue is added to depress any of the tin sulfidesthat were formed during sulfidization.

The invention is further illustrated by the following examples.

EXAMPLE I Hematite Z+270Mesl1 8.0

Ottawa Sand l50+200 Mesh 40.0 A medium-grade tln concentrate producedfrom Catav1 tin ore (Bolivia) by gravity concentration was sulfidizedwith H S gas in a fluid bed at 580-600 C. for 90 minutes. Theconcentrate then assayed: Sn-9.0l%, Fe (tomb-23.09%; S-l1.50%; and Fe(soluble in HCl )8.35%.

5 A sample of the mineral mixture (300 parts by weight) with theaddition of 6 parts by weight of coke was sulfidized in a fluid bedvertical reaction tube by heating at 7l0-740 C. for The Ore sepalratedmagneucan! The tallmgs from 90 minutes in a stream of nitrogen. The useof coke was an atthe magnetlc concentratlon were then floated at aboutpertempt to reduce the cassiterite to o and then sulfidize the centsolids at a pH of 7.7-8.1 (the pH varied during flotation) l0 s o withthe Sulfur released from pyrite Although the bed for 5 minutes w1th 3.2mg. of Aerofloat per liter of water in the was barely moving, a definitesegregation by weight was pulp. Dowfroth was used as the frother, asneeded. A tin froth served in the bed during the heating period. Thefohowihg is concentratfer rich f Snszv resulted the assay of a sample ofthe product:

After this flotation, the pH of the pulp was adjusted with H 80, to 4.9and enough potassium amyl xanthate added to l 5 make a concentration of2.4 mgJl. H O. Frother was added as 2" needed. A pyritic-tin sulfideconcentrate was made. The tin Fe (Total) sulfides were SnS Sn S and SnS.Time for flotation was 5 Fe (sol HCI) 25.66%;and i Sn (sol HCl) 0.35%.

The last flotation step was to adjust the tailings pulp of the 20 abovestep, with H SO.,, to pH 2.7. Then enough potassium The assay of thissample when compared to the assay of a samamyl xanthate was added togive a concentration of 18 mg /1 ple of the same mineral mixturesulfidized with hydrogen sul- Frother was added as needed. Time forflotation was 5 fide at 580 to 600 C. shows that the percent of acidsoluble minutes. The concentrate contained SnS as the predominant n nindication of the amount of reacted is somewhat tin mineral. 2 5 lowerin the sample in which sulfldization of cassiterite was at- The resultswere as follows. tempted by the sulfur release from pyrite.

TABLE II Separation of tin from medium grade concentrate sulphldlzed at580-600 C.

Aero- Percent Sn Percent Fe KAX, float, Percent Step pH mgJl. mg./1.Product wt. Assay Recovery Assay Recovery 7. 09 2.77 2.04 61.93 19.012.92 49.30 66.20 14. 37 8.0 35.26 2.04 7.50 44.94 68.7 9.68 21.36 21.58 8.02 3.3 35. 05 0. 73 2. 68 0. 65 1. 0 100.0 9.62 23.09 Combined tinconcentrate. 22.6 37.2 87.78 11.6 11.3

No'm.KAX=p0tass1um amylxanthate. Aerofloat=thlophosphate collector.

EXAMPLE II A 60 part by weight sample of the heated mineral mixture wasseparated dry into magnetic and nonmagnetic portions. The nonmagneticportion was floated at a pH value of about 5.0. The collector was 3.5mg./l. potassium amyl xanthate (3.0 to 4.0 mg./l.). This lowconcentration was used in order to float the remaining iron sulfides.Any tin sulfides remaining (Sn s and SnS) could then be floated at a pHof about 2.8 with high xa lthate concentration-18 mg./l. 16 to 20 mg./l.

To show the separation of essentially nonmagnetic iron sulfides from tinsulfides, in another flotation test on sulfidized tin ores, thefollowing product was obtained in the second step of flotation, at pH 5,under conditions shown in the previous 45 test: Sn-25.6 percent; Fe16.8percent.

This concentrate was conditioned 5 minutes with 18 mg./ 1. (in water)potassium amyl xanthate at pH 5 with mg./1. glue (Darling Co., Chicago,Black Stripe Glue). Dowfroth was The s ns are 5 9 added as a frother, asneeded. Flotation time used was 5 minutes, but flotation was very rapid,and probably less time would have sufficed. The results were: AssayRecovery G ade Reco ery Product Wt Sn Fe Sn 7: Fe

Mag. Conc. 27.9 3.21 57.42 11.1 57.0 Iron Concentrate (Froth) Sn 17.23%23% Frmh 1 (PH 51)) H1) 373 5451 45 215 Iron Concentrate (Froth) Fe45.73% 98% Froh 2 (PH 18) [L7 13'72 45 2 5 g UD9 1F l7 P f Bl V 30-37%77% Residual Pulp 49.4 9.35 1.45 57.7 2.6 Cmwemme (PulP) Fe 031% 2% Feed(calc.) 2.05 27.99 100.0 100.0 Heads (calculated) Sn 25.6% Heads(calculated) Fe 16.8%

EXAMPLE I The results show that little concentration of tin has beenaccomplished but that 97.4 percent of the iron has been To demons ratethe separation of tin from iron using pyrite separated. The tailingswere carefully inspected under the as a sulfur source, a mixture ofminerals, comprising highmicroscope. This inspection showed that thecassiterite in the g a cassltel'lte, pyrl hematite, n wa quartz sand wastailings was, in the main, unreacted, or at best very little prepared inthe weight proportion similar to a cassiterite table 1. W

concentrate obtained from Catavi, Bolivia. This proportion The test wasrepeated using additional amounts of pyrite. was as follows: 5

Thirty-eight parts by weight of pyrite were added for each parts byweight of themineral mixture. The mixture, after Mineral Size heating at7 l0-740 C. for 90 minutes was sampled and the analysis was:

Cussilcritc 200+270 Mesh 15.0 Pyrite +270 Mesh 37.0 75 Sn (1018i) 7.59%;

S 24.18%; Fe (total) 31.75%; Fe (sol HCl) 25.63%; and Sn (sol HCl 0.38%.

Magnetic and flotation test procedures were followed with this sample,similar to those described in the preceding test. The results aresummarized as follows:

The results show that there was little concentration of tin but that94.5 percent of the iron has been separated. The material in theresidual pulp was observed under the microscope and, again, there werelarge amounts of unreacted cassiterite. The separation results shownindicate that most of the hematite and pyrite have reacted enough tobecome magnetic.

These tests indicate the possibility of upgrading hematitecassiteriteconcentrates by sulfiziding with elemental sulfur (either as elementalsulfur or derived from pyrite) and, or, hydrogen sulfide, and to formthe least amount of sulfidized cassiterite. Most of the iron isrecovered by magnetic separation, and the pyrite iron sulfide byflotation into the froth phase. Any sulfidized cassiterite tending tofloat into the froth is depressed by glue. The remainder, in the pulp,is the low iron cassiterite concentrate.

While it is well known that metal ions such as copper, lead, silver andmercury activate various sulfide minerals it is not too well known norpracticed that certain metal ions depress various minerals. 1n thecourse of the work leading to the present invention, it was found thatmanganese, iron and nickel ions in particular depress tin sulfide. Inparticular, the following tests were performed.

EXAMPLE IV A tin concentrate from Potosi, Bolivia was mixed with Ottawaquartz sand. The total was mixed in the proportions of parts by weightof Potosi concentrate with 40 parts by weight of sand for each flotationtest. The Potosi concentrate contained about 40 percent tin. The oreswere sulfidized with H 8 for 1 hour in a horizontal quartz tube, staticbed. The sulfidized mixture was then floated with distilled water in theusual manner.

The base comparison of whether the metal ions are of value or ahindrance is a test repeated many times which yielded the followingtypical results:

pH 8.8 with Na CO Tin recovery 54.8 percent Concentrate grade 6.85percent This test is indicative of what can be expected when thesulfidized material is floated immediately after sulfidization withoutany further treatment prior to flotation nor any addition of metal ions.

lf copper sulfate is added to the extent of 1 lb. per ton of ore, thefollowing results have been obtained:

Tin recovery 81.0 percent Concentrate grade 13.5 percent tin With leadions added in the form of lead acetate, 1 lb. per ton of ore, at a pH of9, a tin recovery of 77 percent and a tin concentrate grade of 8.0percent was obtained.

With manganese added in the form of manganese chloride at 1 lb. per tonof ore, at a pH of8.5 a recovery of 18.8 percent tin and a tinconcentrate grade of 8.25 percent tin was obtained.

With ferrous chloride added to the extent of 1 lb. per ton of ore at apH of 8.5, a recovery of 9.8 percent tin with a concentrate grade of9.85 percent tin, was obtained.

The addition of nickel sulfate in place of iron chloride, to the extentof 1 lb. per ton ore yielded a tin recovery of 8.3 percent and aconcentrate grade of 10.0 percent. The pH in this case was 6.2.Similarly using ferrous chloride at a pH of 6.7, the tin recovery was16.5 percent with a concentrate grade of 15.5 percent.

The addition of antimony chloride to the extent of 1 lb. per ton of oregave a recovery of 32.5 percent with a concentrate grade of 10.0 percentand a pH of 8.5. At a pH of 6.2 the antimony chloride addition gave arecovery of 19.5 percent and a concentrate grade of 17.2 percent.

For manganese chloride the change from a pH of 8.5 to 6.1 gave a tinrecovery of 6.0 percent with a concentrate grade of 8.4 percent Sn.

The change of cobalt nitrate from a pH of 8.8 to a pH of 6.2 yielded atin recovery of 10.4 percent and a concentrate grade of 14.0 percent.

Nickel sulfate at 1 lb. per ton of ore and a pH of 8.5 gave a recoveryof 22.7 percent and a concentrate grade of 20.5 percent.

From this it can be seen that the presence of various ions can bedeleterious to tin sulfide flotation. 1n particular, ferrous ion isextremely deleterious and it is precisely this ion that is present,after sulfidizing of tin ores, to the detriment of subsequent flotation.

We claim:

1. A method of beneficiating crushed and ground tin oxide orescontaining iron which method comprises:

A. sulfidizing the ore by heating at elevated temperatures in thepresence of a source of sulfur to produce stable tin sulfides: SnS- Sn Sand SnS,

B. subjecting the sulfidized ore to magnetic separation to removemagnetic iron sulfide, and

C. subjecting the sulfidized ore from which magnetic iron sulfide hasbeen removed to progressive and selective flotation to recover a firstflotation concentrate containing predominantly SnS a second flotationconcentrate containing the balance of SnS along with Sn S and SnS and athird flotation concentrate containing Sn S and SnS.

2. A method according to claim 1 further characterized in thatsulfidization is carried out in the presence of reactive sulfur vapor inthe absence of air at a temperature below about 600 C. to convert tinoxide predominantly to SnS 3. A method according to claim 1 furthercharacterized in that the sulfidized ore from which magnetic ironsulfide has been removed is subjected to flotation first under alkalineconditions and then under acid conditions.

4. A method according to claim 3 further characterized in that saidsulfidized ore is pulped and subjected to a first flotation treatmentunder alkaline conditions, between about pH 7.5 to 9 to separate a firstconcentrate which is predominantly SnS 5. A method according to claim 4further characterized in that said pulped ore is conditioned with athiophosphate organic flotation promoter.

6. A method according to claim 1 further characterized in thatsulfidization is carried out in the presence of sulfur vapor in theabsence of air at a temperature above about 600 C. to convert tin oxidepredominantly to Sn S and SnS and thereafter the Sn S and SnS are soakedin sulfur vapor below about 600 C. to convert the same predominantly toSnS 7. A method according to claim 6 further characterized in thatsulfidization is carried out by heating pyrite in the absence of air ata temperature above about 700 C. to preferentially sulfidize iron oxidein the ore.

8. A method according to claim 7 further characterized in that thesulfidized ore from which iron sulfide has been removed is subjected toflotation treatment under acid conditions between about pH 4.5 to 5.5 tofloat remaining iron sulfide.

9. A method according to claim 8 further characterized in that flotationof sulfidized tin oxide is depressed by the addition of glue.

10. A method according to claim 8 further characterized in that the pulpfrom said flotation is acidified to between about pH 2 and 3.5 toseparate a concentrate which is predominantly Sn S and SnS.

11. A method according to claim 8 further characterized in thatflotation of sulfidized tin oxide is depressed by the addition ofmetallic ions selected from the group consisting of iron, nickel,cobalt, antimony and manganese.

12 A method of beneficiating crushed and ground tin oxide orescontaining iron which method comprises:

A. sulfidizing the ore by heating at elevated temperatures in thepresence of a source of sulfur,

B. subjecting the sulfidized ore to magnetic separation to removemagnetic iron sulfide, and

C. subjecting the sulfidized ore from which magnetic iron sulfide hasbeen removed to progressive and selective flotation first under alkalineconditions and then under acid conditions,

1. said sulfidized ore being pulped and subjected to a first flotationtreatment under alkaline conditions, between about pH 7.5 to 9 toseparate a first concentrate which is predominantly SnS- and 2. the pulpfrom said first flotation being acidified to between about 4.5 to 5.5and subjected to a second flotation treatment to separate a secondconcentrate of SnS Sn S and SnS.

13. A method according to claim 12 further characterized in that thepulp from said second flotation is further acidified to between about pH2 and 3.5 and subjected to a third flotation treatment to separate athird concentrate which is predominantly sn s and SnS.

14. A method according to claim 12 further characterized in-that saidsecond concentrate is pulped, conditioned with glue and subjected to afurther flotation treatment at between about pH 4.5 to 5.5 to separatecontaminating iron sulfide in the froth.

15. A method according to claim 14 further characterized in that theiron sulfide from the initial magnetic separation is pulped with saidsecond concentrate before conditioning.

16. A method according to claim 14 further characterized in that the tinsulfide concentrate from said further flotation treatment is mixed withsaid first and third concentrates to produce a final concentrate of tinsulfides.

17. A method according to claim 14 further characterized in that the tinsulfide concentrate from said further flotation treatment is subjectedto further magnetic separation to remove any residual magnetic ironsulfide.

18. A method according to claim 17 further characterized in that theiron sulfide from said further magnetic separation is recycled forfurther sulfidization and flotation treatment.

3 3 a A UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3 ,642 ,464 Dated February 15 1972 Adrian C. Dorenfeld et al It iscertified that error appears in the above-identified patentand that saidLetters Patent are hereby corrected as shown below:

In the Abstract, line 3, "nd" should be --and--.

Column 3, line 40, "agitate" should be -agitated-.

Column 3 line 64, "good" should appear under the column entitled "Acid".

Column 6, line 16, "26.51%" should be "1 .51%".

Column 7, line 54, "base" should be basic-.

Column 9, line 27, before "4.5" --pH-should be inserted.

Signed and sealed this 27th day of June 1 972.

(email) Atbest:

EDWARD M.FLLZTGEEEH,JR- ROBERT GOTTSGHALK Attesting Officer 7Commissioner of Patents

2. A method according to claim 1 further characterized in thatsulfidization is carried out in the presence of reactive sulfur vapor inthe absence of air at a temperature below about 600* C. to convert tinoxide predominantly to SnS2.
 2. the pulp from said first flotation beingacidified to between about 4.5 to 5.5 and subjected to a secondflotation treatment to separate a second concentrate of SnS2, Sn2S3 andSnS.
 3. A method according to claim 1 further characterized in that thesulfidized ore from which magnetic iron sulfide has been removed issubjected to flotation first under alkaline conditions and then underacid conditions.
 4. A method according to claim 3 further characterizedin that said sulfidized ore is pulped and subjected to a first flotationtreatment under alkaline conditions, between about pH 7.5 to 9 toseparate a first concentrate which is predominantly SnS2.
 5. A methodaccording to claim 4 further characterized in that said pulped ore isconditioned with a thiophosphate organic flotation promoter.
 6. A methodaccording to claim 1 further characterized in that sulfidization iscarried out in the presence of sulfur vapor in the absence of air at atemperature above about 600* C. to convert tin oxide predominantly toSn2S3 and SnS and thereafter the Sn2S3 and SnS are soaked in sulfurvapor below about 600* C. to convert the same predominantly to SnS2. 7.A method according to claim 6 further characterized in thatsulfidization is carried out by heating pyrite in the absence of air ata temperature above about 700* C. to preferentially sulfidize iron oxidein the ore.
 8. A method according to claim 7 further characterized inthat the sulfidized ore from which iron sulfide has been removed issubjected to flotation treatment under acid conditions between about pH4.5 to 5.5 to float remaining iron sulfide.
 9. A method according toclaim 8 further characterized in that flotation of sulfidized tin oxideis depressed by the addition of glue.
 10. A method according to claim 8further characterized in that the pulp from said flotation is acidifiedto between about pH 2 and 3.5 to separate a concentrate which ispredominantly Sn2S3 and SnS.
 11. A method according to claim 8 furthercharacterized in that flotation of sulfidized tin oxide is depressed bythe addition of metallic ions selected from the group consisting ofiron, nickel, cobalt, antimony and manganese. 12 A method ofbeneficiating crushed and ground tin oxide ores containing iron whichmethod comprises: A. sulfidizing the ore by heating at elevatedtemperatures in the presence of a source of sulfur, B. subjecting thesulfidized ore to magnetic separation to remove magnetic iron sulfide,and C. subjecting the sulfidized ore from which magnetic iron sulfidehas been removed to progressive and selective flotation first underalkaline conditions and then under acid conditions,
 13. A methodaccording to claim 12 further characterized in that the pulp from saidsecond flotation is further acidified to between about pH 2 and 3.5 andsubjected to a third flotation treatment to separate a third concentratewhich is predominantly Sn2S3 and SnS.
 14. A method according to claim 12further characterized in that said second concentrate is pulped,conditioned with glue and subjected to a further flotation treatment atbetween about pH 4.5 to 5.5 to separate contaminating iron sulfide inthe froth.
 15. A method according to claim 14 further characterized inthat the iron sulfide from the initial magnetic separation is pulpedwith said second concentrate before conditioning.
 16. A method accordingto claim 14 further characterized in that the tin sulfide concentratefrom said further flotation treatment is mixed with said first and thirdconcentrates to produce a final concentrate of tin sulfides.
 17. Amethod according to claim 14 further characterized in that the tinsulfide concentrate from said further flotation treatment is subjectedto further magnetic separation to remove any residual magnetic ironsulfide.
 18. A method according to claim 17 further characterized inthat the iron sulfide from said further magnetic separation is recycledfor further sulfidization and flotation treatment.